8?
Order of Battle - British Fourth Army fictional - HQ Edinburgh
British II Corps (fictional - HQ Dundee)
55th Division (fictional)
3rd Division
58th Division (fictional)
British 113th Independent Infantry Brigade (garrison for Orkney and Shetland Islands)
British VII Corps (fictional - HQ Stirling)
52nd Division
U.S. 55th Division (fictional)
U.S. Ranger battalions
United States XV Corps stationed in Northern Ireland
A careful mix of genuine and artificial units was maintained. Fourth Army was supposedly created from the Northern District, an administrative formation controlling units stationed or training in Scotland.
The 80th Division was also involved in Fortitude at some point.